Print media feed alignment mechanism

ABSTRACT

To maintain quality printed images in high speed photographic quality printing it is necessary to ensure accurate registry of the print media with the printheads. To ensure this result an alignment mechanism is provided for the stack of print media to be fed to the printer. The alignment mechanism comprises a receptacle to hold the stack of print media, a registry stop and a tapping mechanism located opposite the registry stop, to maintain the stack of print media in accurate abutment with the registry stop.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. application Ser. No.10/052,425 filed on Jan. 23, 2002, now issued as U.S. Pat. No.6,619,654, the entire contents of which are herein incorporated byreference.

FIELD OF THE INVENTION

This invention relates to a high speed, photographic quality printer.More particularly, the invention relates to a method of separating asheet of print media from a stack of sheets, the sheets being porous.

BACKGROUND TO THE INVENTION

The applicant has developed various printheads which provide high speed,photographic quality printing. The printheads comprise ink jet nozzlesarranged in an array. The ink jet nozzles are formed usingmicroelectromechanical systems (MEMS) technology. The use of MEMStechnology results in very high speed printing capabilities where pagescan be printed at a rate of up to two pages per second (for double-sidedprinting).

To facilitate such high speed printing, it is important, firstly, thatthe paper fed to the printing station of the printer is accuratelyaligned and capable of the required feed rate with as little likelihoodas possible of paper jams or the like, occurring. Secondly, the papermust be able to be fed to the printing station at a rate sufficient touse the high speed printing capabilities of the printing station to itsfullest extent.

SUMMARY OF THE INVENTION

According to the invention, there is provided a method of separating asheet of print media from a stack of sheets, the sheets being porous andthe method including the steps of:

blowing fluid on to a top surface of a topmost sheet of the print mediaon the stack so that the fluid passes through at least the topmost sheetof the stack; and

capturing at least a part of the topmost sheet for conveyance to aprinting station of a printer.

The method may include blowing the fluid on to the top surface of thetopmost sheet through an aperture means of a pick up means of a printmedia feed arrangement. The pick up means may be in the form of a pickup bar. The aperture means of the pick up bar may be in any of a numberof different forms. For example, the aperture means may be in the formof a channel extending longitudinally along the bar. Instead, the barmay support a plurality of longitudinally spaced, discrete orifices, theorifices defining the aperture means.

The method may include, initially, prior to capturing said at least partof the topmost sheet, lifting said at least part of the topmost sheetfrom the stack. The method may include causing said lifting of said atleast a part of the topmost sheet by creating a low pressure regionbetween a face of the pick up means and the top surface of the topmostsheet of print media.

Preferably, the method includes maintaining the pick up means in spacedrelationship relative to the top surface of the topmost sheet of printmedia to cause said low pressure region.

The method may include capturing said at least part of the topmost sheetof print media by the pick up means, preferably by reversing a directionof fluid flow through the pick up means to cause a change from a blowingaction to a suction action.

The method may include conveying said topmost sheet of print media in adirection substantially normal to a direction of flow of fluid blown onto the stack.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described by way of example with reference to theaccompanying drawings in which:

FIG. 1 shows a part of a printer including a print media feedarrangement operated in accordance with the method of the invention;

FIG. 2 shows a three-dimensional view of an input region of the printerincluding part of the print media feed arrangement;

FIG. 3 shows a three dimensional view, on an enlarged scale, of the partof the print media feed arrangement of FIG. 2;

FIG. 4 shows a schematic, sectional side view of an initial stage ofoperation of the print media feed arrangement;

FIG. 5 shows a schematic, sectional side view of a second stage ofoperation of the print media feed arrangement;

FIG. 6 shows a schematic, sectional side view of a third stage ofoperation of the print media feed arrangement; and

FIG. 7 shows a schematic, sectional side view of a fourth stage ofoperation of the print media feed arrangement.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring initially to FIG. 1 of the drawings, a part of a printer isillustrated and is designated generally by the reference numeral 10. Theprinter 10 is a high speed printer which prints both sides of printmedia at the rate of approximately one sheet per second or two pages persecond (i.e. both sides of the sheet). The print media is, in this case,in the form of a stack of sheets. For ease of explanation, the inventionwill be described with reference to the print media being a stack of A4sheets of paper and, more particularly, sheets of paper having apredetermined degree of porosity.

The printer 10 uses a pair of opposed page width printheads 12, arrangedat a printing station 13, to print on both sides of sheets of paper fedthrough the printing station 13. Each printhead 12 is in the form of amicroelectromechanical systems (MEMS) chip having an array of ink jetnozzles to achieve the high speed, photographic quality printingdesired.

The printing station 13 includes a set of primary rollers 14, comprisinga drive roller 16 and a driven roller 18, arranged upstream of theprintheads 12 to convey a sheet of paper to the printheads 12. Asecondary set of rollers 20, comprising a first roller 22 and a secondroller 24, is arranged intermediate the printheads 12 and the set ofprimary rollers 14. A paper deflector 26 is arranged between the sets ofrollers 14 and 20.

As illustrated more clearly in FIG. 2 of the drawings, the print mediais, as described above, arranged in a stack 28. The stack 28 is receivedin a bin (not shown) of the printer 10 and is retained against a metalbulkhead 30 of the printer 10 in a suitable cabinet (also not shown). Atapping mechanism 32, which is solenoid driven, taps the paper stack 28to ensure that the sheets of the paper stack 28 are maintained inaccurate abutment with the metal bulkhead 30 so that, when a sheet isfed is to the printing station 13, as will be described in greaterdetail below, the sheet lifted from the stack 28 is aligned to be inregister with the printheads 12. In other words, the tapping mechanism32 inhibits skewing of a sheet picked from the stack 28.

The printer 10 includes a paper feed arrangement 34 for feeding a sheetof paper from the stack 28 to the rollers 16 and 18 of the set ofprimary rollers 14 so that the sheet of paper can be transported to theprinting station 13 for printing.

The feed arrangement 34 comprises a pivot rod or axle 36 which isrotatably driven by a drive means in the form of a stepper motor 38. Aswing arm 40 is arranged at each end of the axle 36.

The paper feed arrangement 34 includes a pick up bar 42 which isconnected to a fluid hose 44. The pick up bar 42 is pivotally attachedto the swing arms 40. An arm 46, having a bifurcated end (not shown)projects from one end of the bar 42. The arm 46 is slidably received ina sleeve in the form of a pivot block 48. The arm 46 and, moreparticularly, its bifurcated end, cooperates with an optical sensor 50to determine when the pick up bar 42 is in its home position, the homeposition of the pick up bar 42 being shown, schematically, in FIG. 4 ofthe drawings.

As described above, the printer 10 is a high-speed printer which has acapacity to print at the rate of one sheet per second. To make use ofthis capability, it is important that the sheets of paper are fedindividually to the printing station 13 from the stack 28 in anaccurate, controlled manner. Consequently, it is necessary for the pickup bar assembly 34 to separate a sheet to be transported to the printingstation 13 from the stack 28 accurately. To separate a topmost sheet28.1 from the stack 28, the fluid hose 44 is connected to a fluid source(not shown). Air is blown down the hose 44 in the direction of arrow 52as shown in FIG. 4 of the drawings. The air exits through an outletaperture 54 of the pick up bar 42 as shown by the arrows 56. The air isforced between a foot portion 58 of the pick up bar 42 and the topmostsheet 28.1 of the paper stack 28.

The invention is intended particularly for use with print media which isporous such as, for example, 80 gsm paper.

Due to the porosity of the paper, air is also driven through the topmostsheet 28.1 and impinges on a sheet of the stack 28 which is second fromthe top, as shown by arrow 60 in FIG. 5 of the drawings. This results inan initial separation of the topmost sheet 28.1 from the remainder ofthe sheets of the stack 28.

Also, as a result of localised low pressure occurring between aperiphery of the foot portion 58 of the pick up bar 42 and the topmostsheet 28.1 of the stack 28, the topmost sheet 28.1 is attracted to thepick up bar 42 as shown in FIG. 6 of the drawings. Due to the passage ofair through the topmost sheet 28.1 separation of the topmost sheet 28.1from the remainder of the sheets of the paper stack 28 is aided.

Once the sheet 28.1 has been lifted off the stack 28 and transported ashort distance from the stack 28 and when the pick up bar 42 reaches apredetermined altitude relative to the stack 28, the direction of flowof the air is reversed so that a suction effect is imparted at theaperture 54 of the pick up bar 42. This is shown in FIG. 7 of thedrawings by arrows 62.

As the swing arms 40 of the paper feed arrangement 34 continue to rotatein the direction of arrow 64 (FIG. 3 of the drawings), the pick up arm42 moves in the direction of arrow 66 (FIG. 7) so that a leading edge ofthe topmost sheet 28.1 of the paper stack 28 is fed between the rollers16 and 18 of the set of primary drive rollers 14. The suction is thenshut off in the hose 44 so that the sheet 28.1 is released from the pickup bar 42 for onward conveyance by the sets of rollers 14 and 20 to theprinting station 13 for printing purposes.

It will be appreciated that the airflow parallel to a surface of thetopmost sheet 28.1 of the stack 28 results in a low friction cushionwhich facilitates translational motion of the sheet 28.1 relative to thepick up bar 42. This allows the sheet 28.1 to be moved by any suitablemethod in a direction normal to a face of the pick up bar 42 withouthindering the picking action of the pick up bar 42. It also facilitatesmaintaining a trailing portion of the sheet 28.1 in spaced relationshiprelative to the stack 28 while the sheet 28.1 is being fed to the set ofrollers 14.

The applicant has found that the velocity of air through the fluid hosein the initial, “blowing” direction is not critical, nor is the spacingbetween the pick up bar 42 and the topmost sheet 28.1 of the paper stack28. Further, the weight or grade of the paper of the stack is also notcritical provided that the paper in the stack has a degree of porosity.

Typically, a pressure of approximately 5 kPa is present in the fluidhose 14 when the air is blown on to the paper stack 28. The air isdelivered at approximately 11/s and exits the gap between the footportion 58 of the pick up arm 42 and the topmost sheet 28.1 at apressure of approximately 1 kPa at a velocity of approximately 50 m/s.Experimentally, the pick up arm 42 has been held at a spacing of between0.1 mm and 0.2 mm above the paper stack 28 to pick up the topmost sheet28.1 and this has been found to be successful. In addition, the paperfeed arrangement 34 has been found to operate with paper of a grade from40 gsm to high resolution, photo-quality ink jet paper.

The aperture 54 of the pick up bar 42 can also be any suitable shape.For example, the aperture 54 could be in the form of a straight or wavychannel extending the length of the pick up bar 42. Instead, theaperture could comprise a plurality of discrete nozzles arranged atspaced intervals along the length of the pick up bar 42.

The applicant has found that, surprisingly, by blowing air on to thepaper of the stack 28 separation of the sheets is facilitated. This isan entirely counter-intuitive approach as one would expect that asuction-type mechanism would operate better. However, provided the paperof the stack 28 is porous, very good separation of the topmost sheet ofpaper from the stack 28 can be effected.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A printer comprising: a printhead; a manually refillable receptaclefor holding a bulk source of sheet material in a stack; a feedermechanism for feeding individual sheets from said stack to saidprinthead for printing by said printhead onto said individual sheets;and a sheet alignment mechanism, said sheet alignment mechanismcomprising: a registry stop located at the egress of the receptacle; anda tapping mechanism located opposite the registry stop to tap the stackof sheet material in said receptacle, thereby maintaining the stack ofsheet material in accurate abutment with said registry stop and ensuringthat individual sheets are fed from said stack to said feeder mechanismin correct alignment; a pick up mechanism; a gaseous pathway having anopening into said pick up mechanism; and control mechanism to firstlysupply a gaseous flow through said flow pathway onto the uppermost sheetof said stack, so as to penetrate said porous sheet and separate saidsheet from the stack, and to secondly reverse the flow of air throughthe said flow pathway to hold said uppermost sheet against the said pickup mechanism, and to then move said pick up mechanism to move saidcaptured sheet to a feeder mechanism.
 2. The printer according to claim1, wherein the tapping mechanism is solenoid driven.